1. Field of the Invention
The present invention relates to a bi-fuel injector, in particular for combustion engines, as well as to a method of injection.
2. Background of the Invention
In general, bi-fuel injectors are used for injecting or for supplying various liquids in devices such as, e.g., internal combustion engines, air conditioning units, a moistening apparatus or reformers in fuel cells.
In internal combustion engines or combustion engines, fuel and a liquid additive are injected into the combustion chamber of an internal combustion engine so as to reduce pollutant emission of the internal combustion engine, and if applicable, to increase its efficiency. Such a bi-fuel injector is for example disclosed in German Patent Application No. 197 46 489 A1 which describes a bi-fuel nozzle for injection of diesel fuel as well as a liquid additive, such as e.g. water, into a combustion chamber of an internal combustion engine. Several 2/2-way valves arranged outside the actual nozzle body regulate the conveyance of fuel into, and out of, a pressure chamber. When the fuel is conveyed out of the pressure chamber, liquid additive can flow into the pressure chamber via a check valve and is thus made available for injection.
For example, in order to further reduce pollutant emission of combustion engines and to comply with increasingly stringent limiting values and statutory standards, it is necessary to take into account the cold start emission of motor vehicles, including passenger motor vehicles. Furthermore, an improvement in cold-start behavior and in operation during the warm-up period is desirable.
One approach to achieving this is to divide the fuel into a component which is injected during cold starting resulting in optimal results during the warm-up period, and a fraction which is supplied when the engine is warm.
Approaches followed up to now have provided two separate injection valves in order to supply the various liquids or fuel fractions or fuels to the respective devices, for example to the combustion chamber of the engine. This is however associated with the disadvantage in that it requires considerable space and that there is insufficient space, e.g. in the intake manifold, to direct both injection valves directly to the inlet valves of the engine. In other words, the position achieved is not optimal, which in turn leads to impaired efficiency. Furthermore, this approach is very costly.
Attempts have thus been made to supply both liquids, in particular both fuels or types of fuel, via one injection valve. This is however associated with the problem that there is insufficient space in the valve itself for active switchover.
By contrast, if separation into shutoff valves is effected outside the injection valves, then large residual volumes of the liquid to be shut off prevent quick switchover, or in the case of combustion engines, prevent effective pollutant reduction in the cold-start phase. In other words, the volumes of the pipes and the injection valves up to their exit apertures may for example still contain fuel unsuitable as a starting fuel. But in the case of combustion engines, pure starting fuel should be available right from the first injection stroke, so as to achieve effective pollutant reduction in the cold-start phase.
It is an object of the present invention to create a bi-fuel injector which is particularly suitable for combustion engines and which allows quick switchover when different liquids and/or fuels are supplied. For example when applied in combustion engines or internal combustion engines, a more effective pollutant reduction particularly in the cold-start phase is to be achieved by the invention. Furthermore, a method of injection is to be disclosed which allows a quick changeover of liquid so that e.g. pollutant reduction in particular during cold start of a combustion engine can be effectively reduced. According to a further aspect, high reliability is to be ensured.
Characteristics and advantages of the present invention which have been provided in the following description of the bi-fuel injector, also may apply to the method of injection according to the present invention. Furthermore, characteristics and advantages provided in the description of the method of injection, also may apply to the bi-fuel injector according to the present invention.
The bi-fuel injector according to the present invention, which e.g. is suitable for combustion engines, comprises a nozzle body with a nozzle exit, a moveably held valve needle for opening and closing the nozzle exit, a first supply channel for supplying a first liquid to the nozzle exit, a second supply channel for supplying a second liquid or a liquid additive to the nozzle exit, as well as a slide gate which is arranged in a chamber of the nozzle body and which is hydraulically operable, and which depending on its position, either connects the first supply channel or the second supply channel to the nozzle exit.
The bi-fuel injector according to the present invention makes it possible to supply two different liquids and/or different types of fuel via a single injection valve. This results in particular in an effective reduction of pollutants, especially in the cold-start phase of a combustion engine. A quick change between liquids is possible with high reliability. During cold starting for example, pure starting fuel is available from the very first injection stroke. The volumes in the injection valve up to the exit apertures are very small. Furthermore, injection can take place in an optimal position, resulting e.g. in more effective combustion and more effective pollutant reduction. Costs are significantly reduced not only because there is no need for a second injection valve for the second liquid or for the second fuel, but also because there is no need for an expensive control system for example via additional valves. The bi-fuel injector is particularly reliable because there are no control systems or complex components susceptible to failure, or alternatively such control systems are reduced to a minimum.
Preferably, the slide gate is designed as a ring-shaped piston and the chamber in which the slide gate is located is e.g. a toroidal chamber. This saves additional space and allows economical design which is advantageous especially for series production.
Preferably the slide gate separates the first liquid from the second liquid or the first fuel from the second fuel or from the liquid additive. Mixing of the various liquids or fuels is avoided in this way, and the slide gate can e.g. be designed so as to be effective as a result of the pressure differential between the two liquids or fuels, which for example are located on opposite sides of the slide gate.
Preferably, targeted leakage or a leakage gap for the return flow of the first liquid is provided, so as to flush the bi-fuel injector during activation of the slide gate. This also results in the selected liquid being available immediately, so that for example during cold starting of an engine, a cold-start fuel is injected from the very beginning. Preferably there is an aperture or a gap to this effect between the valve needle or the valve needle head and the respective guide, with liquid or fuel, located between the slide gate and the nozzle exit, being able to flow back into the first supply channel if the second supply channel is connected.
Preferably, the slide gate can be moved between a first position and a second position, whereby in the first position the second supply channel is closed by the slide gate while the first supply channel is open; and in the second position the first supply channel is closed by the slide gate while the second supply channel is open.
For example, the chamber in which the slide gate is located is connected to the first supply channel by a first aperture, and to the second supply channel by a second aperture, with in particular, a further aperture being provided to the nozzle exit, and with the slide gate, depending on its position, closing off either the first aperture or the second aperture. In this way, a particularly effective and reliable switchover of liquid supply or fuel supply takes place in the bi-fuel injector or in the injection valve, while the design is economical.
The slide valve is e.g. slidable as a result of the pressure in the first supply channel and/or by the pressure in the second supply channel. There is thus no need for an active switchover mechanism, e.g. through electromagnetic activation. This saves space and costs. The system can for example be designed such that an increase in pressure of the second fuel or of the second liquid or of the liquid additive results in activation of the slide gate so that the first liquid or the first fuel is shut off while the second liquid or the second fuel is injected. When the pressure of the second liquid is reduced again, e.g. the pressure of the first liquid predominates, causing the slide gate to return to its home position, thus blocking supply of the second liquid. In this position of the slide gate, the first liquid or the first fuel is then injected. In other words, the slide gate can be moved by the pressure differential between the two liquids.
Preferably the slide gate comprises one or several sealing rings so that a very effective separation between the two liquids or fuel types can take place.
It is thus not possible for fuel to seep through between the slide gate and a wall of the chamber in which it is located.
It is particularly advantageous if the slide gate comprises molded-on sealing lips, as this considerably reduces the friction between the slide gate and the wall of the chamber.
Advantageously, the valve needle comprises radial apertures or drill holes for admitting the first liquid from the interior of the valve needle into the chamber containing the slide gate. During operation, the first liquid or the fuel can thus flow through the valve needle and enter the chamber of the slide gate via the radially arranged drill holes. This results in a particularly even and effective supply of liquid or fuel, with the valve needle working precisely and reliably.
Preferably, the slide gate is made of one material and/or of one component. It is advantageous if the slide gate is arranged in the front region of the valve needle, so that the volume or dead volume between the slide gate and the nozzle exit is small when compared to the supply channels, so that as a result of this e.g. only a small volume is flushed through.
In the method of injection according to the invention, depending on operational requirements, either a first liquid or a second liquid is injected or supplied to a combustion chamber of an internal combustion engine, with a slide gate being activated by a pressure differential between the first liquid and the second liquid, with said slide gate causing a switchover between, two supply channels in a bi-fuel injector. In this way, e.g. fast switchover and effective reduction of pollutants can take place, in particular during the cold-start phase of the combustion engine. By switching over the liquid or fuel supply in the bi-fuel injector itself, only small undesirable volumes are contained, so that the respective optimal liquid or optimal fuel is injected directly after switchover. The method does not require any expensive valve control systems or switchover devices outside the injector or the injection nozzle, so that as an additional advantage costs are saved, there is no requirement for a lot of space, and high reliability is achieved.
Preferably the second liquid is a liquid additive or a second fuel which is for example supplied during start-up of the combustion engine or during the warm-up period of the combustion engine. This considerably improves cold-start behavior and reduces pollutant emission which is particularly significant during engine start.
Advantageously, during switchover, a fuel or a liquid to be shut off is forced back against the direction of supply, thus resulting in a return flow. This further reduces the undesirable volume. In particular the return channel is shut off after a lead time. Furthermore, when switching between the supply of liquid or fuel and liquid additive, rinsing can take place during a lead time.
Preferably, the lead time for rinsing and/or for the return flow of liquid or fuel to be shut off is less than a second, in particular preferably less than 0.5 seconds i.e. the lead time is e.g. no longer than the time required for activating a starting device of the combustion engine. In this way it is ensured that e.g. from the time of turning an ignition key to the start position and thus from the start of a starter motor, a starting fuel is available and can be injected without any delay right from the beginning.
In the method of injection, the slide gate can be moved from a first position to a second position by pressure impingement of the liquid or the fuel and/or the liquid additive. During this action the slide gate opens up a connection between a supply channel and a nozzle exit, while closing a connection between a further supply channel and the nozzle exit.
Preferably, the liquid additive is a second fuel with a lower boiling point than that of a first fuel, with the second fuel being injected during cold start. Advantageously, the fuel is cracked on board to a low-boiling component and a high-boiling component using a reactor. In this way, the tank needs to be filled only with a single fuel, while it is nonetheless possible for injection to take place with the fuel component that is optimal for the respective operational state.
The design of the bi-fuel injector which forms a so-called bi-fuel injection valve, is such that it can be used without any modification, for example on the induction pipe engine instead of a traditional injection valve. If necessary, only the fuel system will have to be adapted.
The low-boiling fuel fraction supports ignition more readily and is therefore injected during cold start.
The principle of switchover according to the invention can thus not only be used for injectors of internal combustion engines but also for other types of switchable injectors. For example such a bi-fuel injector and the method of injection can be used in fuel cells, to inject a medium.